had an elevated number of teratological diatom valves, but the 

 percentages here were much smaller than they were at the upper 

 two sites on the Blackfoot River (Table 6) . These resulted in 

 ratings of moderate impairment and fair biological integrity at 

 PoorC-01 and PoorC-02. This impairment is probably due to 

 elevated concentrations of heavy metals. Otherwise, diatom 

 metrics indicated only minor impairment and full support of 

 aquatic life uses in Poorman Creek. 



Diatom diversity and species richness in Poorman Creek 

 increased in a downstream direction, perhaps in response to a 

 decline in concentrations of heavy metals. Slowing current 

 velocities and warmer water temperatures may also contribute to 

 an increase in diatom diversity. A slightly elevated siltation 

 index indicates minor impairment from sedimentation at PoorC-02 

 (Table 6) . 



Most of the major diatom species in Poorman Creek are 

 sensitive to pollution (Table 6) . Pollution index values for 

 Poorman Creek were relatively low for a mountain stream and were 

 about the same at all three sites. The one major species present 

 that is somewhat tolerant of organic enrichment- -Synedra ulna-- 

 was most abundant at the upstream site (PoorC-01) . In Table 6, 

 the similarity index indicates a much greater floristic change 

 occurred between the upper and middle sites (26% similar floras) 

 than between the middle and lower sites (52% similar floras) . 



Arastra Creek. The upper site on Arrastra Creek had a high 

 percentage of abnormal diatom valves (3.67%) that indicates 

 moderate impairment and partial support of aquatic life uses 

 (Table 7) . As with Poorman Creek and the upper Blackfoot River, 

 this impairment was likely due to elevated concentrations of 

 heavy metals. The percentage of teratological diatom valves 

 dropped to an acceptable level at AraC-02. 



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